I think the game is talking about Mem Pak. This is like a memory card for the Nintendo 64 where you insert it in your controller. To set this up, you need to make sure you have the N-Rage's Direct-Input8 V2 1.80a (Plugin) select for controller, -It what I use
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After that follow these steps to set up a mem pak, you will also have to reconfigure your controls!
1) Open up your Project 64 emu.
2) Go to Options
3) Configure Controller Plugin...
4) Press Controller Pak Tab
5) Check RawData
6) Choose MemPak
7) Set the MemPak Directory w/ "Change MemPak Directory"
8) After setting that up, Press New MemPak/Browse
9) Your Done!
*I'm not sure why there is a Gameboy Saves or Rom direcoty in MemPak but probably is a special feature in some games for N64, so make sure u set that up too.